In a digital wireless communication system, a wireless communication device is provided with, for example, an A/D converter (Analog-to-Digital converter) for converting received analog signals, namely wireless packet signals, into digital signals. And since the dynamic range of the input of the A/D converter is finite, the wireless communication device is provided with an automatic gain control device for making an adjustment so that the signal levels of the analog signals to be input into the A/D converter are within the dynamic range.
As a conventional wireless communication device provided with the automatic gain control device and the A/D converter, there is a wireless communication device conforming to the IEEE (Institute of Electrical and Electronics Engineers) 802.11a standard (for example, see Patent Document 1 identified below).
In a conventional wireless communication device 1000 shown in FIG. 42, an AGC (Auto Gain Control) unit 1009 first sets a predetermined gain value in a variable gain amplifying unit 1002.
An analog signal received by an antenna 1001 is amplified by the variable gain amplifying unit 1002, converted in frequency by a frequency converting unit 1003, and converted into a digital signal by an A/D converting unit 1004 (which corresponds to the A/D converter).
Also, a value of power of the analog signal received by the antenna 1001 is detected by an analog signal power detecting unit 1005, and an analog signal indicating the detected value of power is converted into a digital signal by an A/D converting unit 1006.
After an STS detecting unit 1007 detects a short training symbol from the digital signal output from the A/D converting unit 1004, the AGC unit 1009 calculates a gain value to be set in the variable gain amplifying unit 1002 based on the value of power indicated by the digital signal input from the A/D converting unit 1006, and sets the calculated gain value in the variable gain amplifying unit 1002.
After an LTS detecting unit 1008 detects a long training symbol from the digital signal output from the A/D converting unit 1004, the AGC unit 1009 fixes the gain value being set in the variable gain amplifying unit 1002 until a demodulation unit 1010 completes a demodulation of the wireless packet signal.
As described above, the AGC unit 1009 controls the gain of the variable gain amplifying unit 1002 based on the value of power of the analog signal received by the antenna 1001 only when the short training symbol is detected.
Patent Document 1: Japanese Patent Application Publication No. 2003-8676.